The size of an individual display device such as a liquid crystal display (LCD) element is necessarily limited by acceptable manufacturing yields using currently known techniques. It is therefore advantageous to be able to combine several display devices together to produce either a larger display or to mount individual display devices in various positions on a larger display panel. For example in the computer, television and entertainment industries, large area displays of a size much larger than single display device sizes are desired for viewing by groups of people or single individuals. In such applications close placement and alignment of display devices to each other are critical parameters in order to make the edges of the display devices inconspicuous; that is, to insure no breaks are visible as information is viewed across the boundaries from display device to display device. Automotive and aircraft dashboard panels may require information such as speed, temperature, and fuel level to be displayed in various positions, sometimes with large gaps between these positions, on a large overall display panel.
One method of forming a display panel is to clamp individual display elements between two glass plates using screws or other tighteners and brackets of various design about the edges of the glass plates. Individual display elements can then be viewed through one of the glass plates and the display can be illuminated if necessary by placing a light source behind the second glass plate. Such a method is set forth for example in U.S. Pat. No. 4,156,833, said patent incorporated herein by reference. Both the illuminating radiation (hereinafter referred to as light) as well as the display device image must of necessity pass through one or more of the glass plates. Optical properties of the glass plates (such as the transmission/absorption spectrum, and reflectance properties of both surfaces) are critical design parameters which affect display panel performance, possibly causing reductions in brightness, contrast, and resolution. Consequently it is important to select a glass material and surface treatment with care and to minimize the number of layers and interface surfaces through which the images and illuminating light must pass. Obvious variations of this overall structure are possible using optically transparent materials other than glass such as various plastics, or even opaque materials for the back plate in applications where reverse illumination is not needed.
Placing and holding individual display devices in accurate alignment prior to clamping the glass plates together has been difficult to achieve due to extremely precise requirements on alignment accuracy and the possibility of shifting one or more devices previously aligned as others are added prior to clamping all of these in place.
It is also necessary to provide a seal to prevent dust, moisture, or other contaminates from entering the display panel after assembly. Including a seal during clamping adds complexity and difficulty to the clamping process.
Various methods which are the subject of other patents have been developed for making electrical connection to each of the display elements, or for providing electrical interconnection between these. Connections can be made by overlapping edges of display elements as shown in U.S. Pat. Nos. 5,164,853 and 4,408,836 and Japanese Patent JA 0302222 or by abutting corresponding conductive pads on edge surfaces of adjacent display elements as shown in U.S. Pat. No. 5,067,021. The four patents immediately above are incorporated herein by reference. Any of the above or other connection schemes can be employed in the present invention.